This invention relates to a hitch for railroad cars such as an intermodal railcar (e.g., a piggy-back car) wherein the hitch supports an over-the-road trailer on the car with the hitch being movable between an erect position and a retracted position. Specifically, the hitch of this invention relates to a trailer sensor for sensing the presence or absence of a trailer on the hitch, with the sensor allowing retraction of an erected hitch only if no trailer is supported by the hitch.
Trailer hitches for use on intermodal railway cars are well known in the art. Typically, these trailer hitches are used on so-called "piggy back" intermodal railcars to secure over-the-road trailers on the railcar. In recent years, railroads have developed large terminals for handling intermodal shipments in which the trailers are lifted on and off the car either by means of a bridge crane straddling the track, or by means of large fork lifts or the like. In certain applications, to give shippers additional flexibility, such intermodal cars are designed to handle large containers as well as over-the-road trailers. So the railcar may have this dual use capability, it is necessary that the trailer hitch be retractable so as to not interfere with the container when the railcar is used to transport containers. Typically, these retractable hitches are moved from their lowered or retracted position to their erected or raised position through use of a manually operated screw jack mechanism or the like, or by using the crane to lift the retracted hitch.
As an alternative to lift on-lift off loading and unloading, so-called "circus train" intermodal railcars are known in which a tractor having a trailer hitched thereto drives in reverse lengthwise of one or a series of railcars. As the trailer is moved into a desired position, the tractor engages a retracted hitch, lifts it and locks it in its erect position, and effects transfer of the trailer from the tractor to the hitch. To offload a trailer, the trailer is transferred from the hitch to the tractor, after the tractor engages a bumper block on the hitch, so as to initiate retraction of the hitch. With the hitch retracted, the trailer may be driven off the railcar.
Typically, a retractable hitch includes a first or generally vertical strut and a second or diagonal strut. The upper ends of these struts are pivotally connected to a hitch head which serves as a fifth wheel for supporting the front end of the trailer and for positively holding the trailer on the railcar. The hitch head includes releasable jaws or the like for positively engaging the king pin of the trailer. The hitch is typically the only means for holding the trailer in place on the railcar when it is underway. At its destination, the hitch head is actuated so as to release the trailer kingpin, thereby to permit the trailer to be offloaded. Examples of prior art crane operated and tractor operated hitches, and of hitch heads, are shown in the following U.S. Pat. Nos.: 4,185,564, 4,193,350, 4,216,726, 4,221,397, 4,225,276, 4,230,430, 4,230,431, 4,239,429, 4,264,250, 4,397,594, 4,407,617, and 4,563,117.
Heretofore, a manually operable release mechanism has been provided on hitches so a train attendant or yard worker can release the hitch and cause it to retract. In order to do this on some hitches, the person had to be within close proximity to the hitch or the trailer. On many hitches, once the release mechanism is actuated, the hitch is free to fall, by gravity, to its retracted position. Because hitches are heavy, they tend to retract rapidly with great force. Of course, if the hitch is retracted while a trailer is still positioned on the railcar, the fifth wheel support provided by the hitch is no longer available. To avoid this, it would be advantageous to provide a hitch with a sensor which would permit hitch retraction only if a trailer was not supported by the hitch.